Process for increasing the sensitivity of photographic silver halide emulsion



United States Patent Ofi ice 3,137,577 -Patented June 16, 1964 3,137,577 PROCESS FOR INCREASING THE SENSITIVITY OF PHOTGGHIC SILVER HALIDE EMULSRON Yoshio Miura, Fumihiko Nishio, and Akira Kurnai, Ka-

nagawa-ken, Japan, assignors to Fuji Photo Film Co., Ltd, Kanagawa-ken, Japan, a corporation of Japan No Drawing. Filed Feb. 13, 1963, Ser. No. 258,122 Claims priority, application Japan May 23, 1962 3 Claims. (Cl. 96108) This invention relates to photographic materials and particularly to light-sensitive silver halide emulsion having improved sensitivity.

In the preparation of a light-sensitive silver halide photographic emulsion, various methods have been known as so-called chemical sensitization to increase its sensitivity.

For example, it is well-known to increase the sensitivity of photographic emulsion by addition of sulfur C0111- pounds such as allylthiourea, sodium thiosulfate, etc., which contain labile sulfur atoms and capable of reacting with silver salts to form silver sulfide (compounds of these types are also naturally present in gelation), or with reducing agents such as stannous chloride and hydrazine derivatives, or with salts of gold such as aurous thiocyanate, or with combinations of two or more of the aforementioned compounds generally known as chemical sensitizers. (See P. Glafkides, Chimie Photographique, Paul Montel, Paris (1957), p. 297 and p. 301.)

Such chemical sensitizers are believed to form, on the surface of the silver halide, minute amounts of silver sulfide or of silver or of gold, and these processes are capable of increasing the sensitivity of developing-out emulsions by very large factors.

The process of chemical sensitization, however, generally presents some increases of fog, and moreover reaches a definite limit beyond which further addition of sensitizer, or of further ripening with the sensitizer present, merely increases the fog of the photographic emulsion with constant or decreasing sensitivity.

It is also well-known in the art that there is, at the present time, a practical limit to the advantages which can be obtained by the addition of such compounds without presenting deleterious effects such as instability on tropical aging.

We have now found a novel and effective chemical sensitizing method which does not belong to any of the above-mentioned chemical sensitizing methods, but increases the sensitivity of the silver halide photographic emulsion without presenting any increase of fog, and at the same time even improves the stability of the said emulsion on tropical aging. Moreover the novel sensitizers of our invention may be used together with labile sulfur compounds, reducing agents and/or gold compounds, thereby we can further increase the sensitivity of the emulsion.

However, the novel sensitizers of our invention can be used to sensitize photographic silver halide emulsions containing no sensitizers.

According to our invention, we have found that the sensitivity of an ordinary photographic silver halide emulsion can be increased by incorporating therein at least one organo-mercury compound having the following general formula:

COOH

wherein R is an alkyl group having from 1 to 3 carbon atoms, and ripening the said emulsion.

Therefore one object of our invention is to increase the sensitivity of the light-sensitive photographic emulsion without increasing fog.

Another object is to provide photographic emulsion containing the novel sensitizers. Other objects will become apparent from the following description of our invention.

Among examples of the compounds corresponding to the above general formula is 8-(3'-hydroxymercuri-2'- methoxy propyl) 2 oxo 1,2H benzopyran 3 carboxylic acid, which is conventionally named mercumallylic acid (see The Merck Index, 7th edition, p. 649 (1960); and US. Patent 2,667,422).

Inorganic and organic mercury compounds have been known hitherto as additives having stabilizing action, which, when added in minute quantity to a finished silver halide photographic emulsion, reduce its fog without appreciably affecting the sensitivity of the sensitive material, and further maintain the sensitivity and fog of the said silver halide emulsion at or close to initial optimum values under keeping conditions of high temperature and high humidity. (See' e.g. US. Patents 2,728,663- 2,728,667, 2,732,502, 2,751,299, etc.)

The. organo-rnercury compounds represented by the above general formula and used according to the present invention, however, have never been described to be used as additives for photographic emulsion in any patents or literatures. Furthermore, according to the present invention, the organo-mercury compounds are added to the photographic emulsion at any stage of preparing the said emulsion, particularly before and during chemical ripen-' ing, while the organo-mercury compounds disclosed in the above-mentioned patents are added to the finished photographic emulsion before coating, to act as anti.- foggants and stabilizers.

The organo-mercury compounds of our invention are dissolved in water or other solvents which have no harmful effects upon the emulsion, and generally solvents which are miscible with water are to be preferred. In a preferred embodiment, the sensitizer can be dissolved in solvents such as water, methanol, etc., and added to the emulsion in this form.

The particular quantity of the organo-mercury compound used in a given emulsion can vary, depending upon the effect desired, degree of ripening, silver content of the emulsion, etc. The amount used is also dependent upon the particular stage at which the sensitizer is added during the preparation of theemulsion. Although we found that from about 0.05 mg. to about 5.0 mg. of the sensitizer per mole of silver halide is quite adequate to accomplish the desired sensitization of many of the common photographic silver halide emulsions, these limits are merely illustrative.

As supports on which the photographic emulsion prepared according to our present invention is to be coated ordinary supports for photographic emulsion such as glass, cellulose triacetate film base, polyethylene terephthalate film base, barytaged paper, etc. are used.

In addition, the sensitized emulsions of our invention can be used in the preparation of color photographs. This may be accomplished either by using photographic emulsions containing color-forming compounds or couplers which are well-known in the art, or by the use of photographic emulsions which are developed in color developers containing color-forming compounds or couplers also well-known in the art.

The following examples will further illustrate the invention, but it is to be understood that it is not limited thereto.

Example 1 A high-speed negative-type gelatino-silver iodo-bromide photographic emulsion, in which the silver halide consists of 5.0 mole percent silver iodide and 95.0 mole percent silver bromide, is divided into several portions.

One portion is retained as a control and the quantities of mercumallylic acid indicated in the following table are added to the other portions. To each portions, respectively containing 1 mole of silver halide, are then added 10.0 g. of an active type gelatin which is considered to contain natural sulfur sensitizers and 1.0 mg. of HAuCl -4H O and 80 mg. of KSCN dissolved together in an aqueous solution, and the emulsions are ripened at 50 C. for 60 minutes under stirring.

Thereafter, 30 mg. of 1,l'-diethyl-2,2-cyanine iodide, 0.45 g. of chrome alum, and 0.12 g. of saponin are added to the emulsions and the mixtures are coated on cellulose triacetate film base and dried.

These films are exposed on an intensity scale sensitometer to 5,400 K. illumination for 1 second and developed at 20 C. in a developing solution of the following composition:

(3. N-methyl-p-aminophenol sulfate 2.0 Hydroquinone 5.0 Sodium sulfite (anhydrous) 100.0 Borax 2.0 Water to 1.0 litre.

The result is shown in the following table.

Relative sensitivity Gamma Fog Gamma (control) 0.04

Example 2 To a washed full ammoniacal gelatino silver iodo-bromide photographic emulsion containing 1 mole of silver halide, in which the silver halide consists of 2.2 mole percent Agl and 97.8 mole percent of AgBr, there is added 1.2 cc. of a 0.01% methanolic solution of triethylthiourea, 5.0 cc. of a 0.01% aqueous solution of HAuCL; 4H O admixed with 4.0 cc. of a 0.1 N aqueous solution of NH SCN, and thereafter the emulsion is ripened for 40 minutes at 50 C.

To one-half of the ripened emulsion. is added 8 cc. of a 0.001% methanolic solution of 8-(3'-hydroX ymercuri-2'- ethoxypropyl)-2oxo1,2H-benzopyran-3-carboxylic acid,

and thereafter the emulsion is further ripened for l5 minutes at 50 C.

The emulsion thus obtained is added under stirring at 35 C., 0.3 g. of 4-hydroxy-6-methyl-1,3,3a,7-tetraza indene, 0.2 g. of chrome alum and 0.2 g. of saponin, and then the mixture is coated on cellulose triacetate film and dried in the usual manner to produce a thin emulsion.

layer (12 microns).

The other half of the emulsion is handled in like manner except that the solution of the mercury compound is omitted. 4

These two films are exposed on an intensity scale sensitometer to 5400 K. illumination and developed for 4 minutes at 20 C. in a solution of the following composition:

\Vhat we claim is:

1. A process for increasing the sensitivity of photographic silver halide emulsion which comprises, adding to said emulsion at least one mercury compound IEPI'Q sented by the general formula:

(1)12 HO -HgCHrCH-$Ha --COOH wherein R is an alkyl group having from 1 to 3 carbon atoms, and ripening said emulsion.

2. A process according to claim 1, wherein a labile sulfur compound, in addition to said mercury compound, is added to said emulsion.

3. A process according to claim 1, wherein a labile sulfur compound and a gold compound, in addition to said mercury compound, are added to said emulsion.

No references cited, 

1. A PROCESS FOR INCREASING THE SENSITIVITY OF PHOTOGRAPHIC SILVER HALIDE EMULSION WHICH COMPRISES, ADDING TO SAID EMULSION AT LEAST ONE MERCURY COMPOUND REPRESENTED BY THE GENERAL FORMULA: 